In vitro studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and its subdisciplines are traditionally done in labware such as test tubes, Petri dishes, microtiter plates. Studies conducted using components of an organism that have been isolated from their usual biological surroundings permit a more detailed or more convenient analysis than can be done with whole organisms. In contrast to in vitro experiments, in vivo studies are those conducted in living organisms, including humans, whole plants. In vitro studies are conducted using components of an organism that have been isolated from their usual biological surroundings, such as microorganisms, cells, or biological molecules. For example, microorganisms or cells can be studied in artificial culture media, proteins can be examined in solutions. Colloquially called "test-tube experiments", these studies in biology and their subdisciplines are traditionally done in test tubes, Petri dishes, etc.

They now involve the full range such as the omics. In contrast, studies conducted in living beings are called in vivo. Examples of in vitro studies include: the isolation and identification of cells derived from multicellular organisms in. Viruses, which only replicate in living cells, are studied in the laboratory in cell or tissue culture, many animal virologists refer to such work as being in vitro to distinguish it from in vivo work in whole animals. Polymerase chain reaction is a method for selective replication of specific DNA and RNA sequences in the test tube. Protein purification involves the isolation of a specific protein of interest from a complex mixture of proteins obtained from homogenized cells or tissues. In vitro fertilization is used to allow spermatozoa to fertilize eggs in a culture dish before implanting the resulting embryo or embryos into the uterus of the prospective mother. In vitro diagnostics refers to a wide range of medical and veterinary laboratory tests that are used to diagnose diseases and monitor the clinical status of patients using samples of blood, cells, or other tissues obtained from a patient.

In vitro testing has been used to characterize specific adsorption, distribution and excretion processes of drugs or general chemicals inside a living organism. These ADME process parameters can be integrated into so called "physiologically based pharmacokinetic models" or PBPK. In vitro studies permit a species-specific, more convenient, more detailed analysis than can't be done with the whole organism. Just as studies in whole animals more and more replace human trials, so are in vitro studies replacing studies in whole animals. Living organisms are complex functional systems that are made up of, at a minimum, many tens of thousands of genes, protein molecules, RNA molecules, small organic compounds, inorganic ions, complexes in an environment, spatially organized by membranes, in the case of multicellular organisms, organ systems; these myriad components interact with each other and with their environment in a way that processes food, removes waste, moves components to the correct location, is responsive to signalling molecules, other organisms, sound, taste and balance.

This complexity makes it difficult to identify the interactions between individual components and to explore their basic biological functions. In vitro work simplifies the system under study, so the investigator can focus on a small number of components. For example, the identity of proteins of the immune system, the mechanism by which they recognize and bind to foreign antigens would remain obscure if not for the extensive use of in vitro work to isolate the proteins, identify the cells and genes that produce them, study the physical properties of their interaction with antigens, identify how those interactions lead to cellular signals that activate other components of the immune system. Another advantage of in vitro methods is that human cells can be studied without "extrapolation" from an experimental animal's cellular response. In vitro methods can be miniaturized and automated, yielding high-throughput screening methods for testing molecules in pharmacology or toxicology The primary disadvantage of in vitro experimental studies is that it may be challenging to extrapolate from the results of in vitro work back to the biology of the intact organism.

Investigators doing in vitro work must be careful to avoid over-interpretation of their results, which can lead to erroneous conclusions about organismal and systems biology. For example, scientists developing a new viral drug to treat an infection with a pathogenic virus may find that a candidate drug functions to prevent

As a rookie, he played special teams for the Packers in 1961, who beat the Giants 37–0 in the championship game, the first of five NFL titles for head coach Vince Lombardi. During training camp in 1962, Davidson was traded to the Washington Redskins for a fifth round draft choice, he played there in 1962 and 1963, until he was waived in September 1964 final cuts after not meeting the team's strict weight guidelines. Davidson is best remembered his play with the American Football League Oakland Raiders. Al Davis signed him as a free agent shortly after his release from the Redskins and he thrived as a pass rusher under head coaches Davis, John Rauch, John Madden. Davidson played in Oakland from 1964 through 1972, was part of the league merger in 1970, he was an AFL All-Star in 1966, 1967, 1968. The Raiders won the AFL championship in 1967 and played in Super Bowl II, but were overmatched by the Green Bay Packers. Oakland advanced to the AFL title games the next two seasons but lost to the New York Jets in 1968 and the Kansas City Chiefs in 1969, the league's last game.

A stretched Achillestendon in 1972 kept him on the sidelines that entire season. On November 1, 1970, the defending world champion Kansas City Chiefs led the Raiders 17–14 late in the fourth quarter, a long run for a first-down by Chiefs quarterbackLen Dawson sealed victory for the Chiefs in the final minute when Dawson, as he lay on the ground, was speared by Davidson, who dove into Dawson with his helmet at full running speed, provoking Chiefs' receiver Otis Taylor to attack Davidson. After a bench-clearing brawl, offsetting penalties were called, nullifying the first down under the rules in effect at that time; the Chiefs were obliged to punt, the Raiders tied the game on a George Blanda field goal with eight seconds to play. Davidson's play not only cost the Chiefs a win, but Oakland won the AFC West with a season record of 8–4–2, while Kansas City finished 7–5–2 and out of the playoffs. After the season, the NFL changed its rules regarding personal fouls, separating those called during a play from those called after it.

In 1976, the NFL further modified its rules, explicitly calling out a late hit such as Davidson's as illegal. Davidson's hit on Dawson was not an isolated occurrence. A journalist for The New York Times wrote that Davidson "probably was responsible for more late hits than any other player" of his time, was known for going after the opposing team's quarterback. Davidson embraced this reputation. Three years out of football, Davidson signed with the Portland Storm in early September 1974 midway through the World Football League's inaugural 1974 season. While with the Storm, he lived in his motor home. A late season knee injury in early November ended his playing career. Davidson appeared in a few films including The Black Six, M*A*S*H, Conan the Barbarian, he portrayed Porter the Bouncer in Behind the Green Door in 1972 and a convict football player in Necessary Roughness in 1991. Davidson played himself in Miller Lite ads featuring Rodney Dangerfield, he appeared in the short lived 1976 show Ball Four as a minor-league baseball player named RhinoRhinelander, the 1977 pilot for Lucan and the 1984 TV series Goldie and the Bears.

Davidson appeared in an episode of the 1970s TV series Happy Days as a lumberjack. Following his rookie season with Green Bay, Davidson took his winner's check from the 1961 NFL title game and bought rental property in San Diego, he began 1961 with a Rose Bowl win on January 2 and ended it with an NFL championship on December 31, was married in between. Davidson and fellow Oakland Raider teammate Tom Keating were avid motorcycle riders and completed both a ride from California to the Panama Canal and a four-month, 14,000-mile trip across the United States while with the Raiders. Davidson died of prostate cancer at age 72, he was retired and living in San Diego and was survived by his wife Kathy, daughters Janella and Vicki. Other American Football League players Career statistics and player information from NFL.com · Pro-Football-Reference · Ben Davidson on IMDb

Social promotion is the practice of promoting a student to the next grade after the current school year, regardless of if they learned the necessary material or if they are absent. This is done in order to keep the students with their peers by age, that being the intended social grouping, it is sometimes referred to as promotion based on seat time, or the amount of time the child spent sitting in school. This is based on the enrollment criteria for Kindergarten, being 4 or 5 years old at the beginning of the school year; the intention is for the students to be able to graduate from high school level education before their 19th birthday. Advocates of social promotion argue that promotion is done in order not to harm the students' or their classmates' self-esteem, to encourage socialization by age, to facilitate student involvement in sports teams, or to promote a student, weak in one subject on the basis of strength in the other areas. In Canada and the United States, social promotion is limited to primary education, because comprehensive secondary education is more flexible about determining which level of students take which classes due to the graduation requirements, which makes the concept of social promotion much less meaningful.

For example student can study with his age cohort in social studies but with younger students in math class. In some countries, grade retention is allowed when students haven't learned the necessary material or if they are absent; the opposite of social promotion would be to promote students once they learned the necessary material. This might be called "merit promotion", similar to the concept of a "merit civil service"; the scope of the promotion might be either to the next grade or to the next course in the same field. In a curriculum based on grades, this is called "mid-term promotion". In a curriculum based on courses rather than grades, the promotion is open-ended and is better understood as satisfying a prerequisite for the next course. Supporters of social promotion policies do not defend social promotion so much as say that retention is worse, they argue that retention is not a cost-effective response to poor performance when compared to cheaper or more effective interventions, such as additional tutoring and summer school.

They point to a wide range of research findings that show no advantage to, or harm from and the tendency for gains from retention to wash out. Harm from grade retention cited by these critics include: Increased drop-out rates of repeaters over time This may be proven true by data from studies by Allenseorth, the data recorded by Frey where drop out rates in Minnesota schools for non-repeaters nearly doubled from non-repeaters at 12.4% and to retained student drop out rates jumping to 27.2% No evidence of long-term academic benefit for retained students Increased rates of mental disorders and dangerous behaviors such as drinking, drug-use, teenage pregnancy and suicide among repeaters as compared with performing promoted students. Feeling left out with kids from different age groups, which means that being too old may lead to bullying, having fewer friends, being ridiculed. Critics of retention note that retention has hard financial costs for school systems: requiring a student to repeat a grade is to add one student for a year to the school system, assuming that the student does not drop out.

Some parents worry. Opponents of social promotion argue; when promoted children reach higher levels of education, they may be unprepared, may fail courses, may not make normal progress towards graduation. Opponents of social promotion argue that it has the following negative impacts: Students who have to wait for the end of the school year to move on to more advanced studies are denied present success. Students promoted to a class for which they are known to be unable to do the work are positioned for further failure. Students can have so many easy successes during subsequent years that either their study skills deteriorate or they become so frustrated with banal lessons that they drop out. Students can have many failures during the subsequent years, frustrating for them and may increase the risk of dropping out, their frustration at sitting through "baby classes" can lead to classroom disruptions or the humiliation of others. Their frustration can lead to classroom disruptions, it sends the message to all students.

It forces the next teacher to deal with already-prepared and under-prepared students while trying to teach the prepared It gives parents and students a false sense of their children's progress. It creates social fiefdoms of same-age peers, their consequent peer pressure causing bullying and drug abuse; some hold that most students at the elementary school level don't take their education and therefore retention is most not to be effective. Since most middle school students value their education more, retention should be used if they are judged not to have adequate skills before entering high school, it can be argued that social promotion, by keeping most students at the elementary school level from advancing at their own pace, is the reason they don't take their education seriously. Eliminating the social promotion system would make the incentives of merit promotion more effective at the beginning of each student's academic career. In the United States, reten